In recent years, in accordance with advances in new technology for a wide variety of electrical equipment, electric vehicles, hybrid vehicles, robots and the like, performance required for motors or electric generators used liar them becomes highly developed. For example, in industrial motors, electric vehicles, hybrid vehicles, or the like, there is a need for high torque, high output, space-saving and the like.
Accordingly, there is a conventional rotor of a motor disclosed in Patent document 1 as illustrated in FIGS. 20 and 21. FIG. 20 is a perspective view illustrating the rotor and FIG. 21 is a conceptual view illustrating magnetic flux distribution.
The rotor 101 includes a rotor core 105 in which a plurality of magnetic plates 103 having a circular shape as an annular shape are stacked one on another and permanent magnets 109 (hatched parts in both drawings correspond to cross-sections of the magnets extending in a magnetic-plate-stacking direction) held in openings 107 of the rotor core. The rotor 101 is inserted into a stator (not illustrated) that forms a rotation magnetic field so that the rotation magnetic field in the stator according to supplied power interlinks with magnetic flux generated on an outer peripheral surface of the rotor core according to the permanent magnets 109 to rotate the rotor 101 according to repulsion and attraction.
In the rotor 101, if radial widths of magnetic pole portions 103b formed between the permanent magnets 109 and an outer peripheral edge 103a of the magnetic plate 103 are minimized, magnetic resistance with respect to the stator interlinking with the magnetic flux is reduced to increase a magnetic field that is effective in torque. This allows the torque to become higher or the rotor to be downsized if the torque is constant. That is, it is advantageous for increase in torque per motor volume (hereinafter referred to as torque density).
However, the reduction in the radial width of the magnetic pole portion 103b is likely to cause plastic deformation at end corner portions etc. of the opening 107 due to stress concentration based on centrifugal force of the permanent magnet 109 etc, at the time of the rotation, reduces so-called centrifugal strength, and lowers the maximum number of rotation capable of resisting the centrifugal force. As a result, there is a limit on improvement of output per motor volume (hereinafter referred to as output density) and on downsizing.
Further, in the vicinity of the end portion 109a of the permanent magnet 109, there is a problem of inefficient formation of magnetic flux 110 that is formed so as to make a short circuit in the rotor, not to interlink with the stator, and not to contribute to the rotation torque of the rotor.
Further, in the rotor incorporating the permanent magnet 109 having a rectangular cross-section, the magnetic flux distribution caused on the outer peripheral surface becomes a rectangular wave shape including many higher harmonic waves and there is also a problem of increase in higher harmonic iron loss.
Contrary to this, a rotor 111 disclosed in Patent document 2 is proposed as illustrated in FIG. 22.
In the rotor 111, magnetic-flux-controlling portions 119a and 119b are provided at end corners of an opening 117 of a magnetic plate 115 holding a permanent magnet 113 and in a magnetic pole portion 115b so as to thin a thickness of the magnetic plate.
With this, magnetic flux distribution on a surface of the rotor 111 is converted into a sine wave to prevent a torque pulsatory motion.
However, if the magnetic-flux-controlling portions 119a and 119b are formed by etching, no strength is improved and improve in centrifugal strength is not expected.
On the other hand, the magnetic-flux-controlling portions 119a at the end corners of the opening 117 may be formed by hardening portions like Patent document 3.
However, the shape of the magnetic-flux-controlling portions 119a of Patent document 2 is not preferred for higher torque density, higher output density and downsizing and there is a limit on downsizing due to the reduction of the width of the magnetic pole portion 115b.     PATENT DOCUMENT 1: JP2003-304670A    PATENT DOCUMENT 2: JP2012-105410A    PATENT DOCUMENT 3: JP2004-7943A